1. Field of the Invention
The present invention relates to line light sources and image sensors using the same and, more particularly to a line light source of an image sensor which can be used for an image inputting portion of a large image input/output apparatus of a size exceeding A3 (JIS (see Japanese Industrial Standard) B0191) and an image sensor provided with the same.
2. Description of the Background Art
FIG. 16 is a cross sectional view showing a conventional image sensor 13, and FIG. 17 is a partial view showing a hot cathode fluorescent lamp, which is a line light source 51 of image sensor 13.
Referring to FIG. 16, image sensor 13 includes: a casing (a sensor frame) 19 holding components therein; the hot cathode fluorescent lamp used as line light source 51; a rod lens array 15 for erect and equimagnification imaging including a plurality of rod lens; a sensor substrate 16; a sensor IC 17 linearly placed on sensor substrate 16; and a glass plate 18 serving as a surface over which a manuscript 14 is transported. A heater 41 is arranged at the periphery of line light source 51.
Referring to FIG. 17, line light source 51 is provided with a glass tube 42, a lead wire 45, and an electrode 44. A fluorescent material is applied to the inner wall of glass tube 42, and glass tube 42 internally includes mercury and an inactive gas (argon, neon and the like). A filament 43 forming a part of electrode 44 is provided, to which an emissive material called an emitter is applied.
Now, the operation will be described. The light from the hot cathode fluorescent lamp passes through glass plate 18, so that manuscript 14 is uniformly illuminated with light. The illumination light is reflected by manuscript 14 in accordance with the shading information of an image to be directed into the rod lens of rod lens array 15 and to sensor IC 17.
Sensor IC 17 accumulates electric charges in accordance with the intensity of the reflected light, and data is output through sensor substrate 16. The vapor pressure of the mercury in the hot cathode fluorescent lamp varies according to the temperature, and the luminance of the hot cathode fluorescent lamp changes by the variation in the vapor pressure of the mercury. Thus, heater 41 is used to keep the temperature of the hot cathode fluorescent lamp constant. The luminance of the hot cathode fluorescent lamp is kept constant by heater 41.
The hot cathode fluorescent lamp emits light by the following operation.
{circle around (1)} A current is applied to electrode 44 through lead wire 45 to preliminary heat filament 43.
{circle around (2)} Thermoelectrons are discharged from the emitter (emissive material) applied to filament 43.
{circle around (3)} The thermoelectrons move toward electrode 44 on the opposite side as attracted.
{circle around (4)} The thermoelectrons collide with mercury atoms as attracted to electrode 44 to produce ultraviolet rays.
{circle around (5)} The ultraviolet rays are directed to the fluorescent material applied to the inner wall of glass tube 42 to produce visible rays.
A light emitting diode, an external electrode rare gas fluorescent lamp or the like is used as a light source of the image inputting portion, instead of the hot cathode fluorescent lamp. However, for a large image inputting portion having a size exceeding A3, the hot cathode fluorescent lamp producing a sufficient amount of light and allowing an illumination length exceeding A3 is used.
The above described structure of the hot cathode fluorescent lamp of the conventional line light source requires heater 41 to keep the ambient temperature of the hot cathode fluorescent lamp and the vapor pressure of mercury therein constant so that the luminance of the hot cathode fluorescent lamp is kept constant, and further requires a control circuit for heater 41. In addition, the use of mercury adversely affects the environment when the hot cathode fluorescent lamp is discarded, and therefore, the mercury should not be used.
An external electrode rare gas fluorescent lamp causing less variation in luminance according to a temperature may be used in place of the hot cathode fluorescent lamp suffering from the aforementioned problems. The external electrode rare gas fluorescent lamp will be described with reference to FIGS. 18 to 21.
FIG. 18 is a side view showing an external electrode rare gas fluorescent lamp. As shown in FIG. 18, a line light source (external electrode rare gas fluorescent lamp) 1 includes a glass tube 2, outer electrodes 4, 5, a lamp holder 8 provided at both ends, and two lead wires 10.
A fluorescent material is applied to the inner wall of glass tube 2, and glass tube 2 internally includes an inactive gas (xenon or the like). Outer electrodes 4, 5 are arranged opposite to each other with glass tube 2 therebetween, each connected to one lead wire 10. Lamp holder 8 is used for holding the external electrode rare gas fluorescent lamp to a contact image sensor.
FIG. 19 is a cross sectional view taken along the line 300xe2x80x94300 of the external electrode rare gas fluorescent lamp shown in FIG. 18. FIG. 20 is a cross sectional view taken along the line 400xe2x80x94400 of the external electrode rare gas fluorescent lamp shown in FIG. 19. FIG. 21 is a graph showing a distribution of illumination light from line light source 1 shown in FIG. 18, where an abscissa represents the position of line light source 1 and an ordinate represents brightness.
The above described external electrode rare gas fluorescent lamp emits light by the following operation.
{circle around (1)} A high frequency high voltage is applied to outer electrodes 4, 5 through lead wire 10.
{circle around (2)} Xenon atoms are discharged to produce ultraviolet light.
{circle around (3)} The ultraviolet light is directed to a fluorescent material applied to the inner wall of glass tube 2 to produce visible rays.
However, the length of the external electrode rare gas fluorescent lamp is limited. This is because the external electrode rare gas fluorescent lamp is mainly used for a copier for which the size of A3 is sufficient and there is little demand for lamps having the size exceeding A3. In addition, a large amount of investment must be put to manufacture large external electrode rare gas fluorescent lamps having the large size exceeding A3. Consequently, external electrode rare gas fluorescent lamps which are large enough to be used for large image inputting portions having a size exceeding A3 are not presently supplied.
The present invention is made to solve the above mentioned problems. An object of the present invention is to provide a line light source which has a luminance stable with respect to an ambient temperature and which can used for a large image inputting portion having a size exceeding A3 by using a rare gas fluorescent while not using mercury, which may adversely affect the environment.
A line light source according to the present invention is provided with the first and second rare gas fluorescent lamps, and a fixing member. The first rare gas fluorescent lamp includes a first hollow body having an inner wall to which the fluorescent material is applied and including an inactive gas in an internal space thereof, and first and second electrodes positioned on the opposite sides of the internal space of the first hollow body. The second rare gas fluorescent lamp includes a second hollow body having an inner wall to which a fluorescent material is applied and including an inactive gas in an internal space thereof, and third and fourth electrodes positioned on the opposite sides of the internal space of the second hollow body. The fixing member fixes the first and second rare gas fluorescent lamps as arranged in the longitudinal direction thereof.
If the first and second rare gas fluorescent lamps are fixed by the fixing member as arranged in the longitudinal direction as described above, the line light source has a total length of the first and second rare gas fluorescent lamps. Thus, even when the rare gas fluorescent lamp is used, the length of the line light source can readily be increased.
Preferably, the fixing member fixes the first and second rare gas fluorescent lamps such that their center lines in the longitudinal direction are substantially aligned.
Thus, the length of the line light source can be increased while uniformly maintaining the luminance of the line light source.
Preferably, the fixing member has a recess receiving one ends of the first and second rare gas fluorescent lamps, and an opening exposing light emitting portions of the first and second rare gas fluorescent lamps.
Having the above described structure, the fixing member can stably fix the first and second rare gas fluorescent lamps such that their center lines are substantially aligned, whereby the length of the line light source can be increased. In addition, the light from a connecting portion of the first and second rare gas fluorescent lamps can be directed to a manuscript of the like through the opening.
The line light source is included in a casing, and the fixing member fixes the line light source in the casing.
As the line light source is fixed to the casing by the fixing member as described above, the line light source can be stably fixed. Especially, when holders at both ends of the line light source and fixing member are used, the line light source can be stably fixed to the casing.
Preferably, the fixing member connects the first and second rare gas fluorescent lamps with a space provided between the first and second hollow bodies.
Thus, even when the first and second hollow bodies are expanded due to the increased in temperature of the first and second rare gas fluorescent lamps, the ends of the first and second hollow bodies would not contact, so that the breakage of the first and second hollow bodies can be prevented. Namely, the breakage of the line light source due to the increase in temperature is prevented.
More preferably, the fixing member is provided with a reflection surface for reflecting light from at least one of the first and second rare gas fluorescent lamps.
Thus, the light from the first and second rare gas fluorescent lamps can be reflected by the reflection surface, so that the luminance at the connecting portion of the first and second rare gas fluorescent lamps can be increased. As a result, a uniform brightness can be obtained over the reading surface of the manuscript.
Preferably, the fixing member includes a protrusion protruding in a direction in which the light from the first or second rare gas fluorescent lamp is directed, and the reflection surface is provided at the protrusion.
Such provision of the reflection surface at the protrusion enables the light from the first or second rare gas fluorescent lamp to be reflected in a forward direction, and also prevents expansion of the directed light. Thus, the luminance at the connecting portion of the first and second rare gas fluorescent lamps can be more effectively increased.
The reflection surface may be provided by making the surface of the protrusion have a color tone with high reflectivity with respect to the light from the first or second rare gas fluorescent lamp.
Thus, the light from the first and second rare gas fluorescent lamps can be reflected by the reflection surface, so that the reflected light is collected and directed to the manuscript or the like.
The reflection surface may be provided by making the surface of the fixing member opposed to the first or second rare gas fluorescent lamp have a color tone with high reflectivity with respect to the light from the first or second rare gas fluorescent lamp.
In this case, the light from the first and second rare gas fluorescent lamps can be reflected by the reflection surface, so that the reflected light can be directed to the manuscript or the like.
An image sensor according to the present invention is provided with the above described line light source. Thus, a content of the manuscript having a size exceeding A3 can be read.
The image sensor preferably includes a casing in which the line light source may be included, and a moving means for moving the line light source. The moving means may move a part or all of the line light source.
Such a moving means allows the position of the line light source to be adjusted, so that the brightness at the reading surface of the manuscript can be adjusted. As a result, a uniform brightness is obtained over the reading surface of the manuscript.
The moving means may move the line light source at least in one of directions (for example in a direction indicated by an arrow in FIG. 6) toward or away from the reading surface of the manuscript.
Thus, when a sufficient brightness is not obtained over the reading surface of the manuscript, the line light source can be moved in the direction toward the reading surface of the manuscript to increase the brightness over the reading surface of the manuscript. When the brightness over the reading surface of the manuscript is too high, the line light source is moved in a direction away from the reading surface of the manuscript to reduce the brightness over the reading surface of the manuscript. In this case, only one end of the line light source may be moved to adjust the brightness over the reading surface of the manuscript.
The moving means may move the line light source to change the illumination intensity over the reading surface of the manuscript.
When the line light source is manufactured by using the rare gas fluorescent lamp, an illumination intensity distribution is caused in a direction along the surface of the line light source. In this case, the line light source is moved (for example in a direction indicated by an arrow in FIG. 7) with respect to the reading surface of the manuscript, for example, so that the line light source is arranged in a direction of different illumination intensity toward the reading surface of the manuscript. Thus, the brightness over the reading surface can be adjusted to provide a uniform brightness.